Home and building break-ins cause big property loss almost every day. Moreover, when an intruder has a surprise encounter with an occupant in a house or building, the intruder or the occupant may act impulsively causing injuries or even deaths. Typical existing security systems rely on contact sensors, glass breakage sensors, vibration sensors, and motion sensors for detecting an intrusion.
A contact sensor works only when the window or door that it monitors is opened by the intruder, while an intruder may just break or even cut the glass on the window or door for an entrance. A glass breakage sensor or a vibration sensor is designed for detecting such an intrusion.
However, false alarms and false negatives are common complaints for glass breakage sensors and vibration sensors. Daily activities and bad weather may trigger such sensors. For example, clashing of dishes may trigger a glass breakage sensor, opening or closing a window or door may trigger a vibration sensor, and a thunder may trigger a vibration sensor too. The common method to deal with false alarms for such types of sensors is to lower their sensitivity, but lowered sensitivity results in those sensors not responsive to delicate intrusions in which intruders skillfully breaks or cuts the window or door.
The last defense in a typical existing security system is motion sensors, which are usually infrared detection sensors. When the other sensors fail to detect an intrusion, the intruder is expected to be detected by the motion sensors installed in the house or building. However, to avoid false alarms on an occupant, the motion sensors are bypassed when there are occupants in a house or building. Therefore, when an occupant is in a house or building, especially when the occupant is not vigilant, such as in sleep, in shower, playing video games, or watching TV, an intruder can circumvent an existing security system and put the occupant in great danger.
U.S. Pat. No. 7,916,018 B2, issued to Eskildsen et al. on Mar. 29, 2011, discloses a system using a motion sensor to detect whether a contact sensor at a window or door is triggered by an occupant opening the window or door, but the system cannot detect an intruder who either enters through an opened window or door or breaks a window or door for an entrance. U.S. Pat. No. 4,963,749, issued to McMaster on Oct. 16, 1990, describes systems doing one-direction infrared detection, but an occupant still triggers the systems when the occupant moves in the direction of intended detection. U.S. Pat. No. 6,348,863 B1, issued to Krubiner et al. on Feb. 19, 2002, claims systems detecting the direction of a movement for identifying an intrusion through a window or door. However, the timing complexity in the systems introduces detection delay and unreliability.